Malleable white cast iron alloys



Claims priority, application Germany Nov. 16, 1953 9 Claims. (Cl. 148-35) The present invention relates to new malleable white hard cast iron alloys and more particularly to malleable white cast iron alloys in which the carbon is in the form of nodular graphite and the alloy is substantially free of cementite.

Malleable cast iron has been produced wherein the cementite in a white hard cast iron alloy (unannealed malleable iron) is decomposed by heating for a long time at a temperature of about 950 C. so that the carbon of the alloy is present essentially in finer condition (as temper carbon). It has been attempted for a long time to lower the necessary annealing time for the decomposition of the carbides as a basis for improving the industrial efficiency in the production of such malleable cast iron.

Attempts have been made to achieve this lowering of the annealing time by increasing the carbon and silicon content of the alloy. This carries with it the danger that upon casting pieces with large cross-section, the carbon in the raw casting is not liberated in the form of cementite but is already present in a form of graphite, which graphite form is disadvantageous from the point of view of me: chanical properties of the final product.

It has further been known to lower the annealing time by keeping the contents of sulfur in the white hard raw casting as low as possible and if necessary in addition to add known nucleus-forming additives such as magnesium and calcium. However, this process was also unsatisfactory from the industrial standpoint.

It is therefore a primary object of the present inven tion to provide for a malleable cast iron whereby all of the above mentioned difiiculties in the production thereof are avoided.

It is another object of the present invention to provide a method of producing an annealed malleable white hard cast iron utilizing relatively short annealing times.

It is still another object of the present invention to provide a method of producing new iron alloys in which the carbon is present substantially completely as nodular graphite and which alloy has excellent mechanical properties due to its pearlitic structure.

It is a further object of the present invention to provide a method of producing high quality white hard annealed malleable cast iron which may be directly cast in the form of a hollow body such as a tube or the like.

Other objects and advantages of the present invention will be apparent from a further reading of the specification and of the appended claims.

With the above objects in view, the present invention mainly comprises as a new composition of matter a malleableized white hard cast iron alloy essentially consisting of iron, between 25-35% by weight of carbon substantially all in the form of nodular graphite, between 1.5-3.0% by weight of silicon and between 0.25-1% by weight of sulfur, the malleableized alloy being substantially free of cementite.

Surprisingly it has been found that the objects of the present invention are achieved if the sulfur content is increased considerably beyond the measure which has been known and customary up to now and when concurrently therewith the tendency of the alloy towards decomposition of the cementite is increased by considerable increase of the carbon and silicon components.

Thus, according to the present invention a shortening States Patent '0 elc e of the annealing time in order to obtain a malleableized cast iron in which the carbon is present in the form of nodular graphite is achieved by utilizing an unannealed malleable casting which contains carbon in an amount of 2.5-3.5 silicon in an amount of 1.53.0% and simultaneously has a high sulfur content of about 0.25-1%. Particularly good results have been obtained when the sulfur content is between 0.3 and 0.5% by weight. Preferably the carbon content is between 2.83.2%, the silicon content between 2.02.5% and the sulfur content between 0.3 and 0.5%. Obviously, it is practical, depending on the thickness of the walls of the piece to be molded to correlate high carbon content with low silicon content and vice versa in order to prevent a precipitation of the primary graphite. The additional iron additives such as manganese and phosphorous may be present in the usual amounts. Preferably the manganese content is not raised above 0.5 in order to prevent excessive formation of manganese sulfide, and the phosphorous content is held preferably below 0.15% in order to attain good mechanical properties.

The melting of the white hard cast iron alloy can be carried out in a suitable melting oven such as a cupola furnace or a blast furnace with the application of a heat: producing charge such as ore mixtures and combustibles.

The formed raw casting according to the present in-. vention which is used for the rapid production of malle able cast iron is preferably before casting treated in known manner, in order to increase the tendency toward graphite formation, with inoculating agents such as 02-05% ferro-silicon, on aluminum, boron, zirconium and the like.

The process of the present invention mainly comprises a method of producing a malleable cast iron substantially free of cementite, comprising the steps of annealing a raw casting iron alloy essentially consisting of iron, between 2.53.5% by weight of carbon, between 1.5-3.0% by weight of silicon and between 0.25-1% by weight of sulfur, and cooling the thus annealed alloy, thereby obtaining a malleable white hard cast iron in which substantially all of the carbon is in the form of nodular graphite and which is substantially free of cementite.

It is an advantage of the present invention that the raw casting alloy despite, and in fact due to its having a sulfur content which is substantially above the hitherto reported maximum, may be annealed at high temperature for a relatively short period of time while obtaining the result that all of the cementite of the structure is decomposed so that after annealing for about one hour at a temperature of about 950 C., a work piece is obtained having a pearlitic structure which is substantially free of primary cementite and wherein the graphite is contained in the form of nodular graphite. As a result thereof, a mate rial is obtained which has a tensile strength in the range between 40 and 60 kg./mm. while the expansion is cor respondingly between 3 and 10%. The annealing temperature according to the present invention is preferably above 900 C. eg between 900 and 1100 C. and most preferably at about 950'1000 C. The annealing time required when annealing the compositions of the present invention at the above temperature is generally only about 1-4 hours, a time of 1 /z-2 hours generally being suflicient when utilizing the preferred temperature range. It is the great advantage of the present invention that because of the special composition of the raw casting alloy it is possible with only a short annealing time at high temperature to obtain a material which is substantially free of cementite and wherein the carbon is substantially completely in the form of nodular graphite.

Obviously it is possible according to the present invention to first subject the raw casting alloy composition of the present invention to a first annealing step which is carried out in the usual manner to obtain a fenitic struc- I 3 ture and to subsequently subject the material which has been subjected to the ordinary ferritic annealing treatment to the rapid annealing at high temperature accordingtothe present invention in order to impart to the material a particularly good ductility. This ordinary ferritic annealing treatment comprises in the first step slowly heating the material during about 45 hours to the annealing temperature of about 870 (3., holding the material at this temperature for a relatively long time e.g. about 50 hours and then slowly cooling to room temperature during about 60 hours. This treatment followed by the rapid annealing of the present invention results in the production of materials having extremely good qualities when utilizing the composition of the present invention.

According to a further embodiment of the present invention the economy of the process can be further increased by utilizing rapid cooling of the white hard cast iron after the high temperature annealing thereof for a short time. This rapid cooling may be carried out by the use of artificially cooled permanent metallic molds.

A particularly valuable application of the present invention resides in the production of high tensile hollow bodies, such as tubes, which can be made from the new malleable cast iron alloys of the present invention, by centrifugal casting in preferably cooled metallic permanent molds and subsequently subjected to an annealing treatment as described.

The following examples are given as illustrative of the present invention, the scope of the invention not however being limited to the specific details of the examples.

Example 1 A raw casting alloy having the following composition:

Percent by weight Carbon 2.5 Silicon 3-0 Sulfur 1 Iron Balance A raw casting alloy having the following composition:

Percent by weight Carbon 3.5 Silicon 1.5 Sulfur 0.25 Iron Balance is cast in a jacketed mold and subsequently annealed by heating at a temperature of about 1050 C. for about 1 hour. The resulting malleable cast alloy has a high tensile strength and contains the carbon solely in the form of nodular graphite.

Example 3 A raw casting alloy having the following composition:

Percent by weight Carbon 3.0 Silicon 2.3 Sulfur 0.4

Manganese 0.3 Phosphorous 0.1

is centrifugally cast in the form of tubes in metallic molds which can be artificially cooled. The thus cast material is annealed by heating for 1 hour at a temperature of 950 C. The resulting tubes have a pearlitic structure and high tensile strength.

. Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore-such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. As a new composition of matter a malleableized white hard cast iron alloy essentially consisting of iron, between 2.5 and about 3.5% by weight of carbon sub stantially all in the form of nodular graphite, between 15-30% by weight of silicon and between 0.3-l% by weight of sulfur, said malleableized alloy being substantially free of cementite.

2. As a new composition of matter a malleableized white hard cast iron alloy essentially consisting of iron, between 2.8-3.2% by weight of carbon substantially all in the form of nodular graphite, between 2.02.5% by weight of silicon and between 0.3-0.5% by weight of sulfur, said malleableized alloy being substantially free of cementite.

3. As a new composition of matter a malleableized white hard cast iron alloy essentially consisting of iron, about 3.0% by Weight of carbon substantially all in the form of nodular graphite, about 2.3% by weight of silicon and about 0.4% by weight of sulfur, said malleableized alloy being substantially free of cementite.

4. Asa new composition of matter a. malleableized white hard cast iron alloy essentially consisting of iron, between 2.8.3.2% by weight of carbon substantially all in the form of nodular graphite, between 20-25% by weight of silicon and between 0.30.5% by weight of sulfur and also containing manganese in an amount of up to 0.5% by weight and phosphorous in an amount less than 0.15% by weight, said malleableized alloy being substantially free of cementite.

5. A method of producing a malleable cast iron substantially free of cementite, comprising the steps of an healing a raw casting iron alloy essentially consisting of iron, between 2.5 and about 3.5% by weight or" carbon, between 1.5-3.0% by weight of silicon and between 0.3- 1% by weight of sulfur at a temperature between about 9004000" 0.; and cooling the thus annealed alloy, there by obtaining a malleable White hard cast iron in which substantially all of the carbon is in the form of nodular graphite and which is substantially free of cementitc.

6. A method of producing a malleable cast iron substantially free of cementite, comprising the steps of subyecting a raw casting iron alloy essentially consisting of iron, between 2.5 and about 3.5% by weight of carbon, between 1,5130% by Weight of silicon and between 0.3- 1% by weight of sulfur to a ferritic annealing treatment at a temperature of about 870 C.; cooling the thus treated alloy; further annealing the thus treated cooled alloy for a short period of time at a high temperature of between about 900 and 1100 C.; and cooling the thus annealed alloy, thereby obtaining a malleable white hard cast iron in which substantially all of the carbon is in the form of nodular graphite and which is substantially free of cementite.

7. A method of producing a malleable cast iron substantially free of cementite, comprising the steps of centrifugally casting a raw casting iron alloy essentially consisting of iron, between 2.5 and about 3.5% by weight of carbon, between 15-30% by weight of silicon and between 0.3-1% by weight of sulfur; annealing the thus cast alloy at a temperature of 900-1100" 0.; and cooling the thus cast annealed alloy, thereby obtaining a. malleable white hard cast iron body in which substantially all Of the carbon is in the form of nodular graphite and which is substantially free of cementite.

'8. A malleableized cast iron consisting essentially of tial amounts of graphite in nodular form distributed between 2.5% and about 3.5% by weight of carbon, bethroughout a matrix of pearlite. tween 1.5% and 3% silicon, and between 3% and 1% sulfur, said malleableized cast iron containing substan- References Cited in the file of this Patent tial amounts of graphite in nodular form distributed 5 UNITED STATES PATENTS flmmghmt a 1,542,440 Drysdale June 16, 1925 9. A malleablelzed cast lron conslstln-g essentially, by 1 657 Schwartz July 19 1927 weight, of iron, between 2.5% and about 3.5% of carbon, between 1.5% and 3% silicon, between 25% and 1% FOREIGN PATENTS sulfur, said malleableized cast iron containing substan- 10 630,138 Great Britain Oct. 6, 1949 

1. AS A NEW COMPOSITION OF MATTER A MALLEABLEIZED WHITE HARD CAST IRON ALLOY ESSENTIALLY CONSISTING OF IRON, BETWEEN 2.5 AND ABOUT 3.5% BY WEIGHT OF CARBON SUBSTANTIALLY ALL IN THE FORM OF NODULAR GRAPHITE, BETWEEN 1.5-3.0% BY WEIGHT OF SILICON AND BETWEEN 0.3-1% BY WEIGHT OF SULFUR, SAID MALEABLEIZED ALLOY BEING SUBSTANTIALLY FREE OF CEMENTITE. 